Resonant actuator systems are used in a variety of different applications, for example, to move optics within cameras by way of example only. Examples of resonant actuator systems may be found in U.S. Pat. No. 6,940,209, titled, “Ultrasonic Lead Screw Motor”; U.S. Pat. No. 7,339,306, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor”; U.S. Pat. No. 7,170,214, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor”; and U.S. Pat. No. 7,309,943, titled, “Mechanism Comprised of Ultrasonic Lead Screw Motor,” which are hereby incorporated herein by reference in their entireties. In these different applications, control over the velocity of operation while at the same time reducing power consumed for extended battery life and component life of the resonant actuator systems often is required.
To maximize the performance of a reduced voltage resonant actuator a full bridge driver could be used as it would double the available supply voltage as seen by the actuator. However, providing only a continuous full bridge output using the full bridge driver for such an actuator with a capacitive load over a wide supply voltage range can make speed regulation difficult as well as stress the electronics with regard to power dissipation as the supply voltage gets higher.
Modulation of pulse width has been used to provide effective regulation of output speed, but unfortunately saves little in power consumption because the switching frequency of full bridge driving switching sequence does not change. Alternately, application of burst mode has been used to effectively regulate speed and also to reduce power consumption, but unfortunately the use of burst mode adds undesirable audio noise to the output of the system.